The high temperature insulating materials pressed into thermal insulating molded articles consist of about 40 to 70 weight % of a finely divided component, such as e.g. pyrogenically produced silica, 20 to 50 weight % opacifier, e.g. rutile or ilmenite and 1 to 10 weight % of a high temperature resistant fiber, e.g. aluminum silicate fibers to increase the mechanical stability. The thermal insulating molded articles likewise can have the structure of plates which have jackets, as for example, for the thermal insulation of tubes or waste gas converters in automobiles.
They are available commercially as dry pressed molded articles (such as e.g. thermal insulating plates) of different densities (200 to 320 g/l) for this purpose usually encased in glass fiber webs (borosilicate glass) in various constructions.
The above-mentioned thermal insulating plates have a high abrasion of material and a low mechanical strength which make impossible a direct working up and assembly of the thermal insulating plates without additional reinforcing material. To solve this problem it is known to embed thermal insulating plates in a jacket of plies of fiber. However, this process requires the expenditure of a large amount of energy, is expensive and has the disadvantage that the jacket melts at a temperature treatment of 500.degree. to 700.degree. C., (German AS No. 2036124).
There is known according to German OS No. 2961606 a process in which various binder systems are intermixed directly in the insulating material and subsequently are hardened thermally or catalytically. This process has the disadvantage that the thermal conductivity of the thermal insulating plates is increased considerably. There results from this a considerable deterioration not only of the insulating effect but also of the thermal stability.
Therefore, it was the problem of the invention to find heat insulating molded articles for thermal insulation in which the mechanical properties are improved by increasing the flexural strength and resistance to abrasion. Thereby, there should not occur a deterioration of the insulating and thermal properties of the thermal insulating molded articles.